The invention relates to the field of semiconductor manufacturing equipment, and more particularly to a mechanism for monitoring the speed of wafer transport to and from a semiconductor processing furnace.
Semiconductor circuit components are normally produced by slicing an ingot of semiconductor material into thin wafers, each of which are then processed to produce many individual integrated circuits. One of these processing steps involves introducing the wafers into a high temperature furnace to effect thermal oxidation, diffusion, chemical vapor deposition (CVD), annealing, etc. For the purpose of batch processing, the wafers to be processed are typically loaded onto a quartz support structure commonly called a boat. A boat loader coupled to the furnace is operative to insert a boatload of wafers into the furnace for heat treatment and remove them therefrom after processing.
Boat loaders for semiconductor processing furnaces have been the subject of several United States patents, such as U.S. Pat. No. 4,624,638, U.S. Pat. No. 4,721,424, and U.S. Pat. No. 6,537,010. Although boat loading systems have been known to those skilled in the art for many years, none has addressed the need for real-time speed monitoring in the transport of a wafer boat. A loaded wafer boat being transported must move as steadily as possible to ensure the safety of the very valuable work product, i.e., the partially processed semiconductor wafers. Without real-time speed monitoring, for example, there is a possibility that a wafer boat can collide with a furnace tube cap due to an unexpected burst of movement. Such accidents can destroy or seriously damage the in-process wafers. Furthermore, the loading and treatment of wafers are highly automated in batch type processes. The transport speed of wafers can influence effective wafer process time accordingly. Under-speed or over-speed transport of wafers may result in excess or insufficient process time, which in turn leads to a poor yield rate. Therefore, what is needed is a real-time mechanism for monitoring the speed of loaded wafer boat transport to and from a semiconductor processing furnace. It is also desirable to protect the costly wafers from damage resulting from abnormalities including under-speed and over-speed problems.